Hi,
Sometimes I use an unlimited download wi-fi connection, other times I tether my mobile phone sharing the mobile data with my laptop, and this last one has usage limit.
Is there a way to set to a wi-fi saved connection as a metered connection, and make the system and apps more conservative, preventing background data usage such as updates or even update checks.

Updates don't happen unless you initiate them and update checks use next to no resources. There's nothing within Mint to do what you want but it really makes little odds. Use of a well tuned add-blocker when surfing will make a massive difference.